High capacity hard disk drives (HDDs) and other magnetic storage devices employ thermally stable fine-grained high coercivity media. The high coercivity media requires write fields in excess of those attainable with current write heads, the performance of which are limited by pole tip saturation and material properties. Energy-assisted magnetic recording techniques overcome the coercivity/write-field conflict. In heat-assisted recording (HAMR), the temperature of the medium in the write zone is elevated to near the Curie point, typically by a laser, easing magnetization by an achievable write field. An alternative method is microwave-assisted magnetic recording (MAMR), in which near-field microwave radiation excites the recording medium at its ferromagnetic resonance frequency, permitting magnetic moment polarity-switching with reduced write fields.
As with most high precision optical systems, the output power of the element assisting the writing process (e.g., the laser) should be well controlled. To this end, a power monitoring transducer is typically included in the HAMR system at or near the write head. Unfortunately, the introduction of additional transducers may increase the number of terminals required in a preamplifier circuit, which increases the overall footprint/size of the preamplifier circuit. Such an increase in footprint/size is undesirable in many memory systems where miniaturization is desired.